Manufacturing industries use many types of machine tools for the production of precision parts. Machine tools include a wide range of vertical/horizontal machining centers and boring mills. The machine tools also include multiple-spindle machining centers that precisely machine or cut parts within a narrow margin of tolerance. Multiple-spindle machines often use a large gantry capable of supporting multiple spindle carriers that use electric motors to drive the spindles. Attached to the spindles are multi toothed cutters that shape the workpiece.
As each spindle turns and cuts a workpiece, tooth impacts from the individual cutter teeth on each spindle can create undesirable forces and torques that are added and subtracted to both the workpiece and the machine tool. If tooth impacts from each individual spindle become synchronized with tooth impacts from one or more of the other spindles, this can result in cutting variations of greater magnitude than intended. In some cases, the forces and torques cause chatter and excessive deflection of the cutter attached to the spindle. One method to reduce the chatter and excessive deflection calls for adjusting the position of the spindles so that the spindles are out of phase by an amount equal to 360 degrees divided by the product of the number of spindles and the number of cutting edges on each spindle. This method is described in U.S. Pat. No. 6,135,682 granted to Paul McCalmont. Previous systems implementing the methods described in the McCalmont patent have sensed the position of spindles using an external position sensor for each spindle, such as a high-precision rotary encoder. Rotary encoders, or any other position sensors, add cost to a machine. Additionally, spindles operate at high rotational speeds and as a result rotary encoders may require high sampling rates to accurately measure the position of a spindle. Such high sampling rates and high rotational speeds can require equipment that is costly and complex to implement.